Biometrics refers to the collection, synthesis, analysis and management of quantitative data on biological communities, such as forests. More recently, biometrics have come to include the study of methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits. Behaviometrics refers to behavioral biometrics such as typing rhythm, gait, signature, keystrokes or mouse gestures, where the analysis may be performed continuously, without interfering with user activities.
Biometrics may be used to identify an input sample, when it is compared to a template, thus identifying specific people by certain characteristics. The user's identity may be authenticated in any one of three ways: by something the user knows (such as a password or personal identification number), by something the user has (a security token or smart card) or by an attribute of the user himself (a physical characteristic, such as a fingerprint, called a biometric), or by something related to the behavior of a person (a behaviometric, such as signature, keystroke dynamics and voice). Strictly speaking, voice is also a physiological trait because every person has a different pitch, but voice recognition is mainly based on the study of the way a person speaks, and thus is commonly classified as behavioral.
Standard biometric validation systems often use multiple inputs of samples for sufficient validation, such as particular characteristics of the sample. This intends to enhance security as multiple different samples are required such as security tags and codes and sample dimensions.
The various biometrics are compared to determine if a human characteristic may be used for particular biometric application. The criteria for comparison may likely include:                Universality —each person should have the characteristic.        Uniqueness —how well the biometric separates individually from another.        Permanence —measures how well a biometric resists aging.        Collectibility —ease of acquisition for measurement.        Performance —accuracy, speed, and robustness of technology used.        Acceptability —degree of approval of a technology.        Circumvention —ease of use of a substitute.TABLE 1A, below, shows a comparison of existing biometric systems in terms of the above criteria. (Modified from Jain, A. K.; Ross, Arun & Prabhakar, Salil (January 2004), “An introduction to biometric recognition”, IEEE Transactions on Circuits and Systems for Video Technology 14th (1): 4-20) A. K. Jain ranks each biometric based on the categories as being either low, medium, or high. A low ranking indicates poor performance in the evaluation criterion whereas a high ranking indicates a very good performance.        
TABLE 1AUniver-Unique-Perma-Collecti-Perfor-Accepta-Circum-BIOMETRICS: sality ness nence bility mance bility vention* FaceHLMHLHL FingerprintMHHMHMH Hand geometryMMMHMMM KeystrokesLLLMLMM Hand veinsMMMMMMH IrisHHHMHLH Retinal scanHHMLHLH SignatureLLLHLHL VoiceMLLMLHL FacialHHLHMHHthermograph OdorHHHLLML DNAHHHLHLL GaitMLLHLHM Ear CanalMMHMMHM(H = High, M = Medium, L = Low)*Note:under “Circumvention” column, “Low” is desirable, instead of “High.” 
Additionally, to attempt to raise security level, two separate mechanisms may be used together in a process called two-factor authentication. Two-factor authentication, however, typically requires costly changes to hardware and infrastructure. Therefore, biometric security is usually relegated to a single authentication method.
Hence, although much is known about various biometrics that may be used for authentication purposes, delivery of heightened biometric security without adding significant encumbrances to the user/retailer/building operator, etc., is still needed.